1. Field of the Invention
The present invention relates generally to the field of marine navigational aids and, more specifically, to horns used by vessels to sound navigational signals.
2. Discussion of the Prior Art
For vessels navigating at sea or upon other bodies of water, certain "rules of the road" or official navigation signals have been established by authorities such as the United States Coast Guard. Each navigational signal consists of a series of horn blasts which a vessel may sound to indicate an intention to make a turn, to leave the dock, a request to open a bridge, etc. Each signal consists of a unique sequence of "short" and "long" horn blasts.
Various problems arise in attempting to adhere to the rules of the road. For example, a helmsman is frequently preoccupied with steering the vessel while simultaneously monitoring various instruments and may, as a result, fail to sound the proper signal or may erroneously sound the wrong signal for the intended maneuver.
Also, in the presence of fog, the rules of the road require that a particular signal be repeatedly sounded according to a precise timing requirement. For example, if fog is present and the vessel is under power and underway, the correct signal is a single "long" blast once every two minutes. Assuming that the vessel's horn is controlled manually, a crew member must manually sound the signal and use a stopwatch or timer to keep track of the elapsed time.
In the prior art, various mechanical devices have been developed to control a vessel's horn or to aid in sounding the horn. Such devices typically include gears or other rotating members which operate to sound a particular horn signal when an operator actuates a lever or other triggering device.
Such mechanical devices, however, exhibit several disadvantages. First, by its nature, a mechanical horn control device is mechanically linked with a particular horn or horn system on a particular vessel and may not be readily adapted for use with other types of horns or other vessels.
Second, most mechanical horn control devices are limited in the sense that they can only sound one or two signals on an automatic basis. Other signals must be sounded manually by an operator, which again increases the potential for erroneous signalling.
Third, although some mechanical horn control devices are capable of repeatedly sounding "fog" signals on an automatic basis, they do not allow an operator to temporarily override the fog signal to sound another signal on demand.